1. Field of the Invention.
This invention pertains to wire welding, and more particularly to apparatus for feeding weld wire to a welding gun.
2. Description of the Prior Art.
MIG welding requires a smooth and constant feeding of consumable weld wire into a weld arc and puddle in order to join metal together. Erratic wire feeding produces weak, poor, and unattractive welds. Erratic wire feeding also causes "burn-back" and frozen tip conditions at the welding gun, which slows the welding process.
Modern MIG welding equipment typically includes a system for supplying the weld wire to the welding gun. For example, the Millermatic 130XP welding machine manufactured by the Miller Electric Manufacturing Company of Appleton, Wis. represented by reference numeral 1 in FIG. 1, utilizes an 8-inch to 12-inch diameter reel or spool 3 on which is wound a long length of the weld wire 5. The prior weld wire spools 3 have been made of fiberboard, plastic, or wood. The weld wire 5 is fed by a pair of pinch rollers of a feed drive 7 through a flexible cable 9 to the welding gun 11. The pinch rollers rotate to pull the wire 5 from the spool 3 and feed it to the gun 11 when the gun is performing a welding operation. The pinch rollers stop pulling and feeding the wire when no welding is taking place.
The spool 3 of weld wire 5 possesses considerable rotational inertia. Consequently, without proper drag on the spool, starting and stopping the feed mechanism 7 during a welding process can induce a coasting of the spool after the pinch rollers stop pulling the weld wire. If the spool does not stop rotating immediately when the pinch rollers stop, the weld wire can unravel from the spool. The unraveled weld wire can produce binding and tangling upon the next advancement of the wire by the pinch rollers. The binding and tangling can lead to erratic wire feeding for subsequent welds. In some cases, an electrical hazard can exist when electrically charged weld wire unravels and contacts the welding machine case to produce arcing.
To prevent the wire spool 3 from coasting and the attendant problems as abrupt stops and starts are imparted to it, it is known to provide a brake/tensioning mechanism to the spool. The above-mentioned Miller Electric welding machine 1, for example, employs a spring loaded friction force to create a drag between a hub 13 and a fixed shaft 15 on which the hub rotates. Also see FIG. 2. The wire spool 3 fits loosely over a tubular section 17 of the hub 13. A small post 19 on a flange 21 of the hub mates with a hole 23 in the spool 3, such that the spool and hub rotate together. That is, the post 9 and hole 23 arrangement prevent backlash between the hub and spool. As the weld wire 5 is fed by the pinch rollers, the constant friction drag on the hub prevents spool coasting and wire unraveling during normal start and stop welding operations.
The prior brake-tensioning mechanism has worked very well over the years and many thousands of them are in current use. However, the prior wire spools 3 with the hole 23 for the hub post 19 are evolving into recyclable steel wheels that are more economical than the prior fiberboard and plastic spools. The new steel wheels are in wire form, and they have no specific diameter hole to fit the hub post. Consequently, using the wire formed wheels reintroduces erratic weld wire feeding, even though the wire formed wheel fits over the friction restrained hub 13 in the same way as the prior spools.